A digital wireless transmitter operates by sending a sequence of data bits to a remote device using any of a variety of transmission means. In many cases, these data bits are in a particular order that must be preserved for them to be properly interpreted at the remote device. For example, if the data bits represent sound and picture in a video stream, the bits at the remote device must be processed in the same order that they were provided to the transmitter for the sound and video to be properly displayed.
One way to accomplish this is to have the transmitter send the data bits via a data stream in exactly the same order that it received them. With this approach, the remote device need only receive the bits and process them in the order that they appear in the data stream to capture the proper ordering of data. Unfortunately while simple to implement, this approach leaves the data stream very susceptible to being disrupted by burst errors.
Burst errors occur when a number of adjacent data bits are corrupted because of a temporary decline in channel performance. This might happen because of a temporary interfering signal, because of an obstruction moving through the channel, because of multipath fading, which results when the signal level drops to the effects of multipath propagation in either a mobile or stationary device, or the like. During this temporary decline in channel performance, a series of transmitted bits will be interfered with causing them to be sent incorrectly. If uncorrected, these bit errors can reduce the quality of the transmitted signal.
Now many devices will have mechanisms in place to correct individual bit errors. For example, forward error correction (FEC) can be used on a bit stream to correct a certain number of bit errors in an ordered bit stream. However, when too many bit errors occur in a close area in the ordered bit stream, then FEC cannot fully reconstruct the original data.
One way to address this problem is to mix up (i.e., permute) the data prior to transmission in a predictable way such that the data can be reconstructed at the remote device. In particular, the data can be permuted such that two data bits that are adjacent in the original data stream are at least a certain number of bits apart in the permuted data stream. The greater this separation length, the more resistant the transmitted data will be to burst errors.
As noted above, burst errors affect adjacent data bits in the transmitted data stream. But if the data is transmitted using permuted data bits, then adjacent bits in the transmitted stream will not be adjacent bits in the original ordered data stream. As a result, the bit errors caused by a burst error will thus be spread out in the reassembled original data stream. And since the bit errors will be spread out, signal processing, such as FEC, can better correct for these errors and reconstruct the original data stream.